/*
 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
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 *
 *
 *
 */

package java.net;

import java.io.ByteArrayOutputStream;
import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.io.CharArrayWriter;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.util.BitSet;
import java.security.AccessController;
import java.security.PrivilegedAction;
import sun.security.action.GetBooleanAction;
import sun.security.action.GetPropertyAction;

/**
 * Utility class for HTML form encoding. This class contains static methods
 * for converting a String to the <CODE>application/x-www-form-urlencoded</CODE> MIME
 * format. For more information about HTML form encoding, consult the HTML
 * <A HREF="http://www.w3.org/TR/html4/">specification</A>.
 *
 * <p>
 * When encoding a String, the following rules apply:
 *
 * <ul>
 * <li>The alphanumeric characters &quot;{@code a}&quot; through
 * &quot;{@code z}&quot;, &quot;{@code A}&quot; through
 * &quot;{@code Z}&quot; and &quot;{@code 0}&quot;
 * through &quot;{@code 9}&quot; remain the same.
 * <li>The special characters &quot;{@code .}&quot;,
 * &quot;{@code -}&quot;, &quot;{@code *}&quot;, and
 * &quot;{@code _}&quot; remain the same.
 * <li>The space character &quot; &nbsp; &quot; is
 * converted into a plus sign &quot;{@code +}&quot;.
 * <li>All other characters are unsafe and are first converted into
 * one or more bytes using some encoding scheme. Then each byte is
 * represented by the 3-character string
 * &quot;<i>{@code %xy}</i>&quot;, where <i>xy</i> is the
 * two-digit hexadecimal representation of the byte.
 * The recommended encoding scheme to use is UTF-8. However,
 * for compatibility reasons, if an encoding is not specified,
 * then the default encoding of the platform is used.
 * </ul>
 *
 * <p>
 * For example using UTF-8 as the encoding scheme the string &quot;The
 * string &#252;@foo-bar&quot; would get converted to
 * &quot;The+string+%C3%BC%40foo-bar&quot; because in UTF-8 the character
 * &#252; is encoded as two bytes C3 (hex) and BC (hex), and the
 * character @ is encoded as one byte 40 (hex).
 *
 * @author Herb Jellinek
 * @since JDK1.0
 */
public class URLEncoder {

  static BitSet dontNeedEncoding;
  static final int caseDiff = ('a' - 'A');
  static String dfltEncName = null;

  static {

        /* The list of characters that are not encoded has been
         * determined as follows:
         *
         * RFC 2396 states:
         * -----
         * Data characters that are allowed in a URI but do not have a
         * reserved purpose are called unreserved.  These include upper
         * and lower case letters, decimal digits, and a limited set of
         * punctuation marks and symbols.
         *
         * unreserved  = alphanum | mark
         *
         * mark        = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
         *
         * Unreserved characters can be escaped without changing the
         * semantics of the URI, but this should not be done unless the
         * URI is being used in a context that does not allow the
         * unescaped character to appear.
         * -----
         *
         * It appears that both Netscape and Internet Explorer escape
         * all special characters from this list with the exception
         * of "-", "_", ".", "*". While it is not clear why they are
         * escaping the other characters, perhaps it is safest to
         * assume that there might be contexts in which the others
         * are unsafe if not escaped. Therefore, we will use the same
         * list. It is also noteworthy that this is consistent with
         * O'Reilly's "HTML: The Definitive Guide" (page 164).
         *
         * As a last note, Intenet Explorer does not encode the "@"
         * character which is clearly not unreserved according to the
         * RFC. We are being consistent with the RFC in this matter,
         * as is Netscape.
         *
         */

    dontNeedEncoding = new BitSet(256);
    int i;
    for (i = 'a'; i <= 'z'; i++) {
      dontNeedEncoding.set(i);
    }
    for (i = 'A'; i <= 'Z'; i++) {
      dontNeedEncoding.set(i);
    }
    for (i = '0'; i <= '9'; i++) {
      dontNeedEncoding.set(i);
    }
    dontNeedEncoding.set(' '); /* encoding a space to a + is done
                                    * in the encode() method */
    dontNeedEncoding.set('-');
    dontNeedEncoding.set('_');
    dontNeedEncoding.set('.');
    dontNeedEncoding.set('*');

    dfltEncName = AccessController.doPrivileged(
        new GetPropertyAction("file.encoding")
    );
  }

  /**
   * You can't call the constructor.
   */
  private URLEncoder() {
  }

  /**
   * Translates a string into {@code x-www-form-urlencoded}
   * format. This method uses the platform's default encoding
   * as the encoding scheme to obtain the bytes for unsafe characters.
   *
   * @param s {@code String} to be translated.
   * @return the translated {@code String}.
   * @deprecated The resulting string may vary depending on the platform's default encoding.
   * Instead, use the encode(String,String) method to specify the encoding.
   */
  @Deprecated
  public static String encode(String s) {

    String str = null;

    try {
      str = encode(s, dfltEncName);
    } catch (UnsupportedEncodingException e) {
      // The system should always have the platform default
    }

    return str;
  }

  /**
   * Translates a string into {@code application/x-www-form-urlencoded}
   * format using a specific encoding scheme. This method uses the
   * supplied encoding scheme to obtain the bytes for unsafe
   * characters.
   * <p>
   * <em><strong>Note:</strong> The <a href=
   * "http://www.w3.org/TR/html40/appendix/notes.html#non-ascii-chars">
   * World Wide Web Consortium Recommendation</a> states that
   * UTF-8 should be used. Not doing so may introduce
   * incompatibilities.</em>
   *
   * @param s {@code String} to be translated.
   * @param enc The name of a supported <a href="../lang/package-summary.html#charenc">character
   * encoding</a>.
   * @return the translated {@code String}.
   * @throws UnsupportedEncodingException If the named encoding is not supported
   * @see URLDecoder#decode(java.lang.String, java.lang.String)
   * @since 1.4
   */
  public static String encode(String s, String enc)
      throws UnsupportedEncodingException {

    boolean needToChange = false;
    StringBuffer out = new StringBuffer(s.length());
    Charset charset;
    CharArrayWriter charArrayWriter = new CharArrayWriter();

    if (enc == null) {
      throw new NullPointerException("charsetName");
    }

    try {
      charset = Charset.forName(enc);
    } catch (IllegalCharsetNameException e) {
      throw new UnsupportedEncodingException(enc);
    } catch (UnsupportedCharsetException e) {
      throw new UnsupportedEncodingException(enc);
    }

    for (int i = 0; i < s.length(); ) {
      int c = (int) s.charAt(i);
      //System.out.println("Examining character: " + c);
      if (dontNeedEncoding.get(c)) {
        if (c == ' ') {
          c = '+';
          needToChange = true;
        }
        //System.out.println("Storing: " + c);
        out.append((char) c);
        i++;
      } else {
        // convert to external encoding before hex conversion
        do {
          charArrayWriter.write(c);
                    /*
                     * If this character represents the start of a Unicode
                     * surrogate pair, then pass in two characters. It's not
                     * clear what should be done if a bytes reserved in the
                     * surrogate pairs range occurs outside of a legal
                     * surrogate pair. For now, just treat it as if it were
                     * any other character.
                     */
          if (c >= 0xD800 && c <= 0xDBFF) {
                        /*
                          System.out.println(Integer.toHexString(c)
                          + " is high surrogate");
                        */
            if ((i + 1) < s.length()) {
              int d = (int) s.charAt(i + 1);
                            /*
                              System.out.println("\tExamining "
                              + Integer.toHexString(d));
                            */
              if (d >= 0xDC00 && d <= 0xDFFF) {
                                /*
                                  System.out.println("\t"
                                  + Integer.toHexString(d)
                                  + " is low surrogate");
                                */
                charArrayWriter.write(d);
                i++;
              }
            }
          }
          i++;
        } while (i < s.length() && !dontNeedEncoding.get((c = (int) s.charAt(i))));

        charArrayWriter.flush();
        String str = new String(charArrayWriter.toCharArray());
        byte[] ba = str.getBytes(charset);
        for (int j = 0; j < ba.length; j++) {
          out.append('%');
          char ch = Character.forDigit((ba[j] >> 4) & 0xF, 16);
          // converting to use uppercase letter as part of
          // the hex value if ch is a letter.
          if (Character.isLetter(ch)) {
            ch -= caseDiff;
          }
          out.append(ch);
          ch = Character.forDigit(ba[j] & 0xF, 16);
          if (Character.isLetter(ch)) {
            ch -= caseDiff;
          }
          out.append(ch);
        }
        charArrayWriter.reset();
        needToChange = true;
      }
    }

    return (needToChange ? out.toString() : s);
  }
}
